Jet nozzle mixer

ABSTRACT

An external jet nozzle mixer ( 20 ) includes identically formed lobes ( 48 ), equal in number those of the internal mixer ( 42 ). External mixer ( 20 ) works with internal mixer ( 42 ), further to mix the engine internal bypass flow with the internal jet engine core flow, to level the disparate exhaust flow velocities, to reduce the peak velocities from the jet engine core and increase the lower bypass velocities of the engine internal bypass flow, and thereby to reduce noise. The internal lobe contours act as lifting flutes, causing mixing of the primary hot and cold flows before exiting the nozzle. The external lobe contours act as venturi chutes, accelerating the cooler ambient air secondary flow. The lobes thus act collectively as an injector to force the cooler ambient secondary flow into the previously mixed primary flow as it exits the nozzle. Also obtained is an increased thrust efficiency and a consequently decreased fuel consumption and engine emissions.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/340,369, filed 7 Dec. 2001.

REFERENCE REGARDING FEDERAL SPONSORSHIP

Not Applicable

REFERENCE TO MICROFICHE APPENDIX

Not Applicable

1. Field of the Invention

The present invention relates to jet nozzle mixers for aircraft jetengines and, in particular, to improvements in effecting a greatercooling and a lower noise level in exhaust gases emanating from suchengines and in increasing power and fuel efficiency.

2. Description of Related Art and Other Considerations

Noise (decibel) level in jet aircraft engines is established by laws andregulations, specifically promulgated by the International CivilAviation Organization (ICAO), Annex 16. At present, commercial jetaircraft weighing over 75,000 pounds (34,000 kilograms) must meet Stage3/Chapter 3 noise (decibel) level requirements which establish anallowable decibel noise level. Under Annex 16 Stage 4/Chapter 4requirements, a lower maximum (decibel) level will be mandated, by atleast a reduction of 10 decibels from current Stage 3/Chapter 3 levels.Such noise reduction is effected by mixing of the primary hot exhaustgases in an internal mixer with secondary bypass cooling air and bybreaking of the single core of exhaust gases into a plurality of smallercores through use of a first set of lobes positioned internally in theengine. For some engines, a second set of lobes in an external mixer ispositioned downstream from the first set at the terminus of the engine.A thrust reverser module is joined to the engine housing at the engineterminus by use of an attendant mechanism covered by the STANG fairing.Because the engine has specifically designed dimensions, the second setof lobes must be configured to accommodate the existing engine design,which has a terminus exit area dimension of 1,100 square inches (7,097square centimeters), rather than to reconfigure the engine to fit thesecond set of lobes. Such engine reconfiguration is impractical andexpensive. Therefore, the direction towards meeting Stage 3/Chapter 3noise requirements has been involved in developing a variouslyconfigured second set of lobes whose design does not always meet suchrequirements and, when the lobe design does, the lobes are difficult andexpensive to manufacture and the mixer is expensive to be retrofitted tothe engine.

Some engines have not employed the use of a second set of lobes or anexternal mixer, specifically one produced by Pratt & Whitney, in theirJT8D-217/219 Series. Currently, this engine includes an internal 12 lobemixer and is only certified to Stage 3/Chapter 3 noise levels. There hasbeen a desire to qualify this particular engine to Stage 4/Chapter 4noise levels, but to minimize the costs of doing so with, preferably, nochanges in its thrust reversal components primarily because of cost andother economic reasons. To bring this engine to Stage 4/Chapter 4 noiselevels, an additional 2 decibel reduction in jet noise is required. Suchan upgrading is a challenge that has not been met.

SUMMARY OF THE INVENTION

These and other problems are avoided and the Stage 4/Chapter 4requirements are both met and surpassed by the present invention, notonly for the above-mentioned Pratt & Whitney JT8D-217/219 Series enginebut also for other engines. The second stage or external jet nozzlemixer of the present invention includes a number of lobes, which areequal in number to those of the first stage or internal mixer, and allof the second stage mixer lobes are identically formed. As the lobesaxially extend outwardly from the mixer attachment to the engine nozzle,they axially inwardly expand from an essentially circular base to anundulating configuration whose apices increase in height. The lobesinclude complex curvatures whose interior and exterior surfaces greatlyenhance mixing respectively of the previously mixed bypass coolingair-hot exhaust gases from the internal mixer and additional ambientcooling air, and thereby also reduce noise. At their terminus, the areaencompassed by the lobes remains essentially the same (1,065 to 1,120sq. inches) as for the jet engine for which it is designed which, forthe Pratt & Whitney JT8D-217/219 Series engine, is 1,095 to 1,105 squareinches (6,089 to 7,097 square centimeters). For other engines, the lobeterminus area is consistent with that of the engine in question.

For the Pratt & Whitney JT8D-217/219 Series engine, for example, theexternal mixer length is 12 inches±3 inches (30.45 cm±8 cm). Theessentially circular base of the lobes at the mixer inlet has a lineardimension of 39.7 inches (101 centimeters) round, providing an area of1,223 sq. inches (7,891 square centimeters). At the mixer outlet at thefull height of the regularly undulating lobes, the dimension of themixer circumscribing the lobes at their greatest height is also 39.7inches (101 centimeters) diameter but, because of the scalloped lobeshape, the area enclosed by the lobes is 1,065 to 1,120 sq. inches(6,089 to 6,403 square centimeters), which matches the area of theexisting tailpipe.

The exit shape has elliptical shaped lobes and is proportional to a10×2.5 ellipse (plus or minus 2 inch major axis, and ±0.5 inch minoraxis). These curve sides help resist distortion caused by the exhaustgas pressure.

Consistent with the above discussion, an important and preferred designparameter is to shape the external mixer of the present invention with agenerally cylindrical configuration and with as short a length aspossible, so that it does not interfere with the existing thrustreverser doors at the end of the tailpipe. As a result, the mixer of thepresent invention permits the use of existing thrust reversers withoutnecessitating any modification thereto. Only a part of the STANGfairings need to be slightly decreased in their inner dimensions toaccommodate the internal mixer. Also, the existing tailpipe is shortenedby about 5 inches (12.7 centimeters).

Functionally, the interior surfaces of the lobes force the impinging hotgases, as previously mixed with the secondary bypass cooling air by thefirst set of lobes of the internal mixer, in all directions towards theinterior of the mixer, essentially 45° C. to 60° C., to effect avigorous mixing of the gases. Simultaneously, additional ambient coolingair is forced from the exterior surfaces of the lobes to mix furtherwith the internally mixed gases. These actions cause the smaller gascores, which were formed by the first stage mixer, to break intoinnumerable forms which are both cooler and considerably noiseattenuated. In part, the internal contours of the lobes act as flutes toproduce a lifting effect which causes the primary hot and cold flows tomix before entering the nozzle. The external contours of the lobes actas chutes which produce a venturi effect and accelerate the coolersecondary flow of ambient air. The lobes thereby act collectively as aninjector to force the cooler ambient secondary flow into the previouslymixed primary flow as it exits the nozzle. These actions further reducethe noise level. Further, the curve sides of the lobes help resistdistortion caused by the exhaust gas pressure. An ameliorative furtherresult is that the accelerated gas/air flow helps to faster move large,previously slowed mixtures to increase the efficiency of the jet engine,by increasing its thrust, that is, an increased thrust specific fuelconsumption (TSFC) is estimated to be about a 3% improvement. Suchincreased TSFC occurs through better dynamic mixing of the bypass or fanduct and turbine exhaust gases. It addresses the problem of the transferfrom a hot, high velocity volume to a cooler, slower velocity volume.This mixing levels the disparate flow velocities attendant with the jetengine exhaust, reduces the peak velocities from the jet engine core andincreases the lower bypass velocities of the jet engine internal bypassflow. Because noise is a function of jet exhaust velocity to the 7^(th)power, and because peak velocities from the core flow are reduced, thejet noise is thereby reduced.

As stated above, the axial length of the mixer of the present inventionis 12 inches±3 inches, which means that there is a lesser distancebetween the nozzle exit and the buckets of the thrust reverser. Theeffect of such decreased distance is that more of the thrust from theengine is captured by the buckets and thus utilized to brake theaircraft when needed.

Several advantages are derived from this arrangement. The jet nozzlemixer of the present invention fits within and is attachable to theexisting engine exit whose area which, as stated above, is 1,095-1,105square inches (6,261-7,129 square centimeters) exit area for the Pratt &Whitney JT8D-217/219 Series engine. The lobes of the present inventioncan be made uniform and easily tailored to provide an efficient mixingof the exhaust gases with the ambient air and the attendant reduction innoise. Its uniform dimensions enables its manufacturing costs to bereduced. The need to modify the existing thrust reverser per se isavoided because the mixer is fittable and attachable to the existingengine exit; only minor dimensional changes in the existing STANGfairing, and tailpipe and outer barrel are required without otherwiseneeding any change in other components such as the thrust reverser, thethrust reverser doors, and their linkages. Efficiency in jet engineoperation is increased, with concomitant saving of fuel and coststhereof. Thrust reverser braking of the aircraft is improved.

Other aims and advantages, as well as a more complete understanding ofthe present invention, will appear from the following explanation of anexemplary embodiment and the accompanying drawings thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a and 1 b are perspective views of an end portion of a jetengine nozzle assembly to which is attached both a thrust reverser and asecond stage external jet nozzle mixer as embodied in the presentinvention.

FIG. 2 is schematic drawing illustrating the interior of the jet engineshown in FIG. 1 with a known first stage internal mixer in the interiorof the engine and the second stage inventive external jet nozzle mixerat the terminus of the engine, including the decrease in distancebetween the jet nozzle mixer of the present invention and the thrustreverser buckets, as compared to its non-use.

FIG. 3 a is a view of the engine and its internal mixer shown in FIG. 2taken along line 3—3 thereof, and FIG. 3 b is a perspective view of thecone and surrounding vanes of the internal mixer.

FIG. 4 is a perspective view of the second stage, external mixerassembly of the present invention in which its twelve identically shapedlobes are seen. The four undulating cross-sections, #1 through #4, whichvariously pass through the lobes of the mixer and which extend from theend of the mixer assembly towards its point of attachment to theterminus of the engine, are representative of all planes which passthrough all of the lobes. A fifth cross-section #5, which is circular,extends about the band which anchors the mixer to the engine terminus. Asixth cross-section #6 is positioned behind the plane of the fifthcross-section #5, and is seen in subsequent figures. These sixcross-sections are referred to in subsequent figures as defining planesnumbered #1-#6.

FIG. 5 is view of the external mixer of the present invention takenperpendicularly to and along the axis of the mixer assembly shown inFIG. 4, and also depicts how the lobes disperse and break up the hotgas/air mixture. FIGS. 5-1 through 5—5 illustrate the areas incorporatedby the lobes at their respective cross-sections #1-#5. Thecross-sections, as portrayed or positioned on the interior surfaces ofthe lobes, define interior mixer areas within their respective planes,respectively of 1,100 square inches (7,097 square centimeters) at plane#1 (FIG. 5-1), 1,110 square inches (7,162 square centimeters) at plane#2 (FIG. 5-2), 1,120 square inches (7,226 square centimeters) at plane#3 (FIG. 5-3), 1,154 square inches (7,445 square centimeters) at plane#4 (FIG. 5-4), and 1,223 square inches (7,891 square centimeters) atplane #5 (FIG. 5—5) which extends into plane 6 for attachment to theexisting Pratt & Whitney JT8D-217/219 Series engine.

FIG. 6 is a side view, taken 90° with respect to the mixer shown in FIG.5, of that mixer and its four undulating cross-sections and fifthcircular cross-section along planes #1-#5. The circular configuration ofthe lobes at plane #5 extends generally cylindrically with the samegeneral diameter to its end at plane #6.

FIG. 7 is an enlarged view of a superimposition of the lobes and thesame previously illustrated four undulating cross-sections and fifthcircular cross-section as shown in FIGS. 4-6.

FIG. 8 is a view of the lobe shown in FIG. 7 looking down upon the apexof the lobe, in which the several cross-sections indicate the varyingcurvature of the lobe as its extends along the mixer axis throughcross-sections or planes #1-#6.

FIG. 9 is a side view of the lobe shown in FIGS. 4-8 and illustrates theseveral lobe curvatures as it extends along the mixer axis, withspecific reference to planes 1-6 with its attaching end to the nozzle ortailpipe.

FIG. 10 depicts the contour lines of a lobe between its planes #1-#6, asviewed looking down upon the lobe.

FIG. 11 is a view of a specific one of the section curvatures shown inFIG. 9 along with hardware for its attachment to the nozzle or tailpipe.

FIG. 12 is a schematic drawing, not to scale, of an engine nozzleassembly and modified STANG fairings for accommodating the jet nozzlemixer embodied in the present invention.

FIG. 13 is a perspective view of one of the STANG fairings as modifiedto accommodate the mixer of the present invention.

FIG. 14 is a graph attesting to the improvement in net thrust versusengine pressure ratio in a Pratt & Whitney JT8D-217/219 Series enginewhen use of the second stage external mixer of the present invention iscompared to that of a standard nozzle, in which the engine pressureratio is defined as the measure of engine exhaust pressure divided byambient pressure.

FIG. 15 is a graph demonstrating the improvement in TSFC (thrustspecific fuel consumption) versus thrust in a Pratt & WhitneyJT8D-217/219 Series engine when use of the second stage external mixerof the present invention is compared to that of a standard nozzle.

FIG. 16 is a graph of preliminary flight test data of aMcDonnell-Douglas MD-80 aircraft as evidence of the improvement in fuelconsumption in terms of NAMPP (nautical air miles per pound of fuel)versus mach in a Pratt & Whitney JT8D-217/219 Series engine when use ofthe second stage external mixer of the present invention is compared tothat of a standard nozzle.

DETAILED DESCRIPTION

Because the present invention was devised particularly with respect tothe Pratt & Whitney JT8D-217/219 Series engine, the following discussionwill be directed specifically thereto; however, it is to be understoodthat the present invention is equally relevant for use in other jetengines and, therefore, is not to be limited to a specific jet engine.

Accordingly, FIGS. 1 a and 1 b illustrate a nozzle assembly 18 relatingto, for example, a Pratt & Whitney JT8D-217/219 Series jet engine towhich a jet nozzle mixer 20 as embraced by the present invention isattached at its exhaust terminus 19. Assembly 18 also supports a thrustreverser having a pair of thrust reverser buckets 22. The attachment ofthe thrust reverser buckets to assembly 20 is effected by bars 24 whichare pivotally linked to a pair of diametrically opposed mechanismshoused within fairings 26, one of which is shown in FIG. 1. The fairingsare secured at opposite sides of the assembly. The thrust reversers andthe linking bars are of conventional design and are unmodified whencoupled with the present invention. The fairings are also ofconventional design, but a part of the structure covered thereby isslightly modified as will be explained below with respect to FIGS. 12and 13.

As shown also in FIG. 2, mixer 20, because of its added axial length, ispositioned closer to thrust reverser buckets 22 when they are deployedas brakes. Such closer positioning is demonstrated by the differentlengths “x” and “y” of FIG. 2. The ameliorative result of such closerpositioning permits the buckets to capture a greater portion of theexhaust for braking purposes than previously obtainable. However, it isimportant that mixer 20 not be located too close to buckets 22 so thatthe flow of the redirected exhaust gases are not adversely affected andthat the doors, linkages and the mixer are not deleteriously stressed.

The internal arrangement of nozzle assembly 18 as secured to a jetengine is depicted in FIGS. 2, 3 a and 3 b. An engine 28 includesturbine blades 30 and compressor or fan blades 31 joined together on acommon shaft 32 within a two-part housing 34 a and 34 b. Forconvenience, the burners preceding turbine blades 30 are not shown. Hotexhaust gases exit from the turbine blades as a core 36. A bypass or fanduct 38 surrounds housing 34 b for affording passage of cooling air, asdenoted by arrow-headed lines 39, from the ambient exterior to firststage or internal jet nozzle mixer 42 of the engine. Core 36 of hotgases is disposed to be mixed with the cooling air within a first stagemixing chamber 40 by use of first stage jet nozzle mixer 42 positionedtherein. As best seen in FIGS. 2, 3 a and 3 b, first stage internal jetnozzle mixer 42 includes two sets of vanes 44 and 46 which arerespectively inwardly and outwardly inclined to direct and mix togetherrespectively the cooling air and the hot gases in chamber 40. Vanes 44and 46 are positioned around a core terminating in a cone 47. As statedabove, consistent with the Pratt & Whitney JT8D-217/219 Series jetengine design, the total of inwardly directed cooling air vanes 44 andoutwardly directed hot gas vanes 46 respectively number twelve each.This resulting admixture divides core 36 into a smaller cooler centralcore and twelve surrounding small cores of mixed hot gases and coolingair of different velocities which, nevertheless, are still extremely hotand produce an unacceptably high noise level. These smaller central andsurrounding cores pass towards terminus 19 of the nozzle assembly forsecond stage mixing and cooling by second stage external jet nozzlemixer 20 of the present invention.

Second stage external jet nozzle mixer 20 and its component parts isillustrated in FIGS. 4-11. Mixer 20 includes twelve identical lobes 48to equal in number the twelve cooling air vanes and the twelve hot gasvanes, and the twelve smaller hot gas cores of the internal mixer. Forease of manufacture, twelve sections, each including a lobe, isfabricated and the sections on either side of the lobes are weldedtogether, such as identified by weld lines 50. Combined, the lobesextend from a circular section through a plurality of increasinglyundulating portions, such as exemplified by cross-sections #1-#6. Thetransition from a round configuration at cross-section #5 to thescalloped or undulated configuration at cross-section #1 is a verysmooth complex curve and, consequently, minimizes airflow distortion anddrag and maximizes the mixing of the hot gases with neighboring air andthereby to reduce noise. This is achieved by using synchronizedcross-sections and a plurality of weighted and blending splines betweenthe cross-sections. Such a design is provided using state-of-the-art CADsoftware.

As stated above, the cross-sections, as portrayed on the interiorsurfaces of the lobes and depicted by shading in FIGS. 5-1 through 5—5,delimit interior mixer areas within the planes defined by thecross-sections, respectively of 1,100 square inches (7,097 squarecentimeters) at plane #1 (FIG. 5-1), 1,110 square inches (7,162 squarecentimeters) at plane #2 (FIG. 5-2), 1,120 square inches (7,226 squarecentimeters) at plane #3 (FIG. 5-4), 1,154 square inches (7,445 squarecentimeters) at plane #4 (FIG. 5-4), and 1,223 square inches (7,891square centimeters) at plane #5 (FIG. 5—5). The cross-sectional areasfrom plane #5 to plane #1 decreases arithmetically, about 5%, 2.5%,1.25%, etc.

The section extending between cross-sections #5 and #6 is an extensionfrom the section adjacent cross-section #5 and is used to affix mixer 20to the nozzle terminating the Pratt & Whitney JT8D-217/219 Seriesengine, and has an equivalent 1,223 square inch (7,891 squarecentimeter) area. An annular reinforcing support band 52 (seeparticularly FIG. 11) joins the lobes at their circularly shaped sectionadjacent cross-section #5, while a band ring 54 is joined to lobes 48 attheir base sections 55 at their greatest undulation at cross-section #1.

FIG. 11 also illustrates the attachment of mixer 20 to nozzle assemblyor tailpipe 18. Specifically, the mixer is secured to terminus 19 of thenozzle assembly and to a doubler ring 70. Both terminus 19 and thedoubler ring are angled outwardly and, compared to prior nozzleassemblies, are shorter by approximately 5 inches.

As shown, for example in FIGS. 7 and 11, the interior surfaces of thelobes force the impinging hot gas-bypass cooling air mixture frominternal mixer 42 in all directions towards the interior of internalmixer 20, that is, essentially 45° to 60° as illustrated by multiplearrow-headed lines 56 in FIG. 5, to effect a vigorous mixing of thegases. At the same time, additional ambient cooling air is forced fromthe exterior surfaces of the lobes to mix further with the internallymixed gases. These actions cause the smaller gas cores from internalmixer 42 to break into myriad forms which are both cooler andconsiderably noise attenuated. In part, the internal contours of thelobes act as flutes or channels 64 to produce a similar aerodynamicaction as the skins of the airplane wings to produce a lifting effect.This lifting effect causes the primary hot and cold flows to mix beforeentering the nozzle. The external contours of the lobes, which act aschutes 66, are designed to act as a multitude of venturis, and thus toaccelerate the cooler secondary flow of ambient air. This arrangementeffectively forms an injector to force the cooler ambient secondary flowinto the previously mixed primary flow as it exits the nozzle. Thisaction further reduces the noise level.

In addition, dimples 72 are formed on both sides of band 54 of theexternal mixer and act as vortex generators to prevent the mixed gasflow from attaching to band 54 and thereby to enhance the mixing action.

This afore-mentioned acceleration also helps to increase the efficiencyof the fuel-air burning in the engine. By producing an increased flow,the exhaust gases are more rapidly exhausted from the engine and therebythe need for the engine and its bypass compressor to expend energy inmoving these gases is alleviated.

In addition, the lobes are elliptically shaped, being proportional to a10×2.5 ellipse, plus or minus 2 inches (5 centimeters) major axis, andplus or minus 0.5 inch (1.3 centimeter) minor axis. These curved sideshelp resist distortion caused by the exhaust gas pressure.

Because mixer 20, such as illustrated in FIGS. 4, 5, et seq., has a1,065 sq. inch to 1,100 square inch (6,089 to 7,097 square centimeters)area encompassed by the lobes at plane #1 and a 1,223 square inch (7,891square centimeters) area at plane #5, where the mixer is joined tonozzle assembly 18, it is possible to use the mixer without anymodification of thrust reversers 22. As a result, it is necessary onlyto slightly reconfigure the structure covered by fairings 26. Suchreconfiguration is depicted in FIGS. 12 and 13, and is effected byremoving only a small portion from each of such structure, specificallythat portion indicated by parallel dashed lines 58. Further, a tongue 59is also removed.

The following points, although not exclusive, may be advanced in summaryof the present invention.

-   -   A. As an important design parameter, the mixer has as short a        length as is possible, e.g., 12 inches±3 inches (30.45 cm±8 cm).        The lobe shape starts with a circular or rounded configuration        at 39.7 inches (101 centimeters) and terminates with a scalloped        or undulated configuration at the same diameter (39.7 inches or        101 centimeters) and an area of 1,065 sq. inches to 1,100 sq.        inches (6,089 to 7,097 square centimeters), which matches the        existing tailpipe area. By keeping the mixer short, it will not        interfere with the existing thrust reverser doors at the end of        the tailpipe.    -   B. The mixer is designed so that it can be attached to the        existing tailpipe with minimum impact on exiting components,        such as the thrust reverser, thrust reverser doors, stang        fairings, outer fairings.    -   C. The mixer has elliptically shaped lobes whose shapes are        proportional to a 10×2.5 ellipse (plus or minus 2 inch major        axis, and plus or minus 0.5 inch minor axis). These curved sides        help to resist distortion caused by exhaust gas pressure.    -   D. The transition in the lobes from a round to a scalloped shape        forms a very smooth curve in order to minimize airflow        distortion and drag and to maximize the mixing of the hot gases        with neighboring air. This is achieved by using six synchronized        cross-sections and many weighted and blending splines between        the cross-sections. The design was achieved using        state-of-the-art CAD software, Surfcam, from Surfware, Inc.    -   E. The cross-sectional area of the mixer, taken along its axis,        decreases arithmetically, about 5%, 2.5%, 1.25%, etc., until its        terminus is reached.    -   F. Rather than simply splitting the air flow, the mixer inner        lobe surfaces ramps the exhaust gases inward and, at the same        time, the outer surface draws outside air into the mixer using a        type of NACA duct (airfoil air scoop) so that, when the hot        gases and the cooling air is mixed, the exhaust noise is        reduced.    -   G. The contour lines of the lobed surfaces form a uniform        initial slope, which is desirable to ensure even pressure as the        exhaust gases are redirected inward.    -   H. Testing of the final lobe shape design with models ensured        that the lobes would be formed with relative ease from a flat        sheet, and with minimum distortion or strain which would be        otherwise caused by material stretching and compressing as the        flat sheet is forced into the desired configuration. Such ease        of formation is amenable to selection of the preferred material        which comprises an aerospace alloy, Inconel 625, a difficult        material to work.    -   I. Twelve lobes are used to match the existing twelve vanes in        the engine that swirl and spin the exhaust gases as they leave        the engine. The twelve “hot spots” inside the tailpipe, which        are produced by the existing vanes, are broken up by the twelve        lobes of the present invention, thereby minimizing any        undesirable hot spots.    -   J. The lobe shape forms a complex compound surface, with as        large as possible employ of radii used at all locations so as to        minimize drag and to allow for the smoothest possible gas flow        redirection.

Preliminary testing of the present invention, as used in a Pratt &Whitney JT8D-217/219 Series jet engine, has disclosed decidedimprovements in performance as compared to conventional technology. Suchdata, as shown in FIGS. 14-16, are based upon present testing. It istherefore to be understood that final test results may evidencedifferent data. Notwithstanding, as shown in these graphicalrepresentations of preliminary test data, the external or second stagemixer of the present invention demonstrates improved performance overthat obtainable with conventional systems.

FIG. 14 discloses that, based upon a reasonable match for all engineparameters, such as engine revolutions per minute (rpm), exhaust gastemperature (EGT) and fuel pump data, the present invention demonstratesan increase in thrust at the mid range of engine pressure ratio (EPR),that is, engine exhaust pressure divided by ambient pressure. Thesetests were conducted by use of the external or second stage mixer of thepresent invention as compared to use of a standard nozzle (Serial Number48099 as detailed in a United Technologies Corporation (UTC) documentfor its Pratt & Whitney engines, entitled “JT8D-209, -217, -217A, -217C,-219, TURBOFAN ENGINES ENGINE MANUAL PART NO. 773128” bearing an initialissue date of Jul. 1, 1979 and revised Nov. 15, 2001.

FIG. 15 reveals that the present invention, within a mid thrust range of7,000 to 15,000 pounds of thrust, improves upon the TFC (specific fuelconsumption) by a factor of approximately 2% to 3%. The followingexample is given to demonstrate the economic benefits obtained byassuming a 2% increase in fuel consumption. An engine average fuel burnof 7,000 pounds of fuel per hour converts into an approximateconsumption of 1,000 gallons per hour of fuel. Based upon an assumedyearly flight usage of a McDonnell-Douglas MD-80 aircraft of about 2,000hours per year, the aircraft consumes about 2,000,000 gallons of fuelper year. At a cost of $1.00 per gallon, the annual fuel cost for suchan aircraft would be $2,000,000. Therefore, for a 2% improvement in fuelconsumption as provided by the present invention, the saving wouldamount to $40,000 per aircraft.

FIG. 16 compares the improvement in nautical air miles per pound of fuel(NAMPP) versus mach number for a McDonnell-Douglas MD-80 aircraftthrough use vis-a-vis non-use of the present invention. Here,preliminary flight data shows an increased NAMPP of the “JET nozzle”over all points on the curve when employing the present invention overits non-use “baseline nozzle.”

It is to be understood that, in the foregoing exposition wheredimensions, areas, etc., are expressed in English system units and,parenthetically, in metric system units, the English unit system shalltake precedence in the event of any error in conversion from the Englishunit system to the metric unit system.

Although the invention has been described with respect to a particularembodiment thereof, it should be realized that various changes andmodifications may be made therein without departing from the spirit andscope of the invention.

1. In a nozzle for a jet engine enclosed within a tubular housing andalso having an existing first stage mixer within said housing whichincludes a number of first stage lobes, and having a thrust reverserhaving a stowed position fixed relative to the tubular housing andhaving a deployed position, the improvement comprising a second stagemixer coupled to the exhaust aperture of said tubular housing to receivegas exhausted from the first stage mixer, said second stage mixer havinga plurality of identically formed lobes which equal in number those ofthe first stage lobes; the second stage mixer being unenclosed by ahousing and having an exterior in contact with the ambient air to allowthe air to enter the mixer and mix with the gas from the first staremixer; the second stage mixer having a trailing edge forming the exitterminus for the gas flow; and said thrust reverser in the deployedposition being positioned downstream of the exit terminus to reverse thegas flow.
 2. The improvement according to claim 1 wherein the existingfirst stage lobes mix hot gases from combustion in the jet engine withbypass air flowing through said tubular housing to diminish the velocityof the hot gases, and in which said second stage lobes have interiorsurfaces which are configured to further mix the mixed hot gas-bypassair mixture and further to level the velocities of the mixed hotgas-bypass air mixture and thereby reduce jet engine noise.
 3. Theimprovement according to claim 2 in which said second stage lobes haveexterior surfaces which are configured to draw ambient air external tosaid tubular housing into mixing with the further mixed hot gas-bypassair mixture and to still further level the velocities of the mixed hotgas-bypass air mixture and thereby further reduce the jet engine noise.4. The improvement according to claim 2 further including dimplescoupled to the terminus of said second stage for acting as vortexgenerators to prevent the mixed gas flow from attaching to said lobeterminus and thereby to enhance the mixing action.
 5. The improvementaccording to claim 1 in which said second stage identically formed lobesare configured (a) on their interior surfaces to force impinging hotgases exiting at said exhaust aperture of said tubular housingsurrounding said jet engine towards the interior of said second stagemixer and (b) on their exterior surfaces to mix with ambient cooling airexterior to said tubular housing to form gas cores which are smallerthan those formed by the first stage mixer and to break the smaller gascores into innumerable forms which are both cooler and noise attenuated.6. The improvement according to claim 5 in which said interior surfacesof said second stage lobes are shaped to accelerate flow of the hotgas-cooling air mixture and thereby to increase the efficiency of thejet engine thrust.
 7. The improvement according to claim 5 in which saidinterior and exterior surfaces of said second stage lobes actrespectively as flutes and chutes.
 8. The improvement according to claim1 in which said second stage mixer lobes increase in height from acircular configuration adjacent to the first stage mixer to anundulating configuration at the terminus of said second stage mixer. 9.The improvement according to claim 8 wherein the jet engine has adimensionally existing terminus exit area defined by said exhaustaperture of said tubular housing, and in which said second stage mixerlobes at the second stage mixer terminus have an area whose dimension isgenerally the same as that of the jet engine terminus exit area.
 10. Theimprovement according to claim 9 wherein the jet engine terminus exitarea and the second stage mixer terminus area are both 1,100 squareinches (7,097 square centimeters).
 11. The improvement according toclaim 9 wherein a preexisting thrust reverser including conventionalthrust reverser doors are secured to a mount rearward of said exhaustaperture, and in which said second stage mixer has an axial length whichis sufficiently short as to not interfere with movement of the thrustreverser doors.
 12. The improvement according to claim 11 wherein thepreexisting thrust reverser and its thrust reverser doors are securedrearward of said exhaust aperture by mechanisms enclosed by STANGfairings, and in which a part of said STANG f airing is slightlydecreased in its inner dimension to accommodate said second stage mixer.13. The improvement according to claim 9 in which said second stagelobes are configured (a) on their interior surfaces to force impinginghot gases from the jet engine towards the interior of said second stagemixer and (b) on their exterior surfaces to mix with ambient cooling airexterior of said tubular housing, to form gas cores which are smallerthan those formed by the first stage mixer and to break the smaller gascores into innumerable forms which are both cooler and noise attenuated.14. The improvement according to claim 13 in which said second stagelobes are elliptically shaped to help resist distortion otherwise causedby pressure of exhaust gasses.
 15. The improvement according to claim 8in which the increase in height of said second stage mixer lobes fromtheir circular configuration to their undulating configuration forms asmooth curve transition to minimize airflow distortion and drag and tomaximize mixing of hot gases from the engine with ambient air.
 16. Theimprovement according to claim 1 in which said second stage mixer isformed from a plurality of secured-together sections, each including oneof said second stage lobes.
 17. The improvement according to claim 1 inwhich said second stage lobes are configured to employ the largestpossible radii for all surfaces thereof to minimize drag and allow for asmoothest possible redirection of gas flow therealong.
 18. Theimprovement according to claim 1 wherein a thrust reverser havingbuckets which are deployable into a thrust-reversing position isoperatively mounted rearward from said exhaust aperture, and whereinsaid second stage lobes have an axial length which decreases thedistance otherwise existing between the exhaust aperture and the thrustreverser buckets when deployed into their thrust-reversing position forenabling increased capture of the thrust by the buckets.
 19. In a nozzlefor a jet engine enclosed within a tubular housing and having a thrustreverser having a stowed position fixed relative to the tubular housingand having a deployed position, and also having an existing first stagemixer which includes a number of first stage lobes enclosed in saidtubular housing rearward from said jet engine a method for coolingexhaust engine exhaust gases and for attenuating engine exhaust noisecomprising the steps of: utilizing a second stage mixer coupled to theexterior of said tubular housing at an exhaust aperture of said tubularhousing; the second stage mixer being unenclosed by a housing and havingan exterior in contact with the ambient air to allow the air to enterthe mixer and mix with the gas from the first stage mixer; the secondstage mixer having a trailing edge forming the exit terminus for the gasflow; and said thrust reverser in the deployed position being positioneddownstream of the exit terminus to reverse the gas flow; the secondstage mixer receiving substantially all of the exhaust from the firststage mixer; utilizing a plurality of identically formed lobes whichequal in number those of the first stage lobes; and configuring saidlobes (a) on their interior surfaces to force impinging hot gases fromthe jet engine towards the interior of the second stage mixer and (b) ontheir exterior surfaces to mix with ambient cooling air communicatedfrom the exterior of said tubular housing to form gas cores which aresmaller than those formed by the first stage mixer and to break thesmaller gas cores into innumerable forms which are both cooler and noiseattenuated.
 20. The method according to claim 19 further comprising thesteps of increasing the second stage mixer lobes in height from acircular configuration adjacent to the first stage mixer to anundulating configuration at the terminus of the second stage mixer. 21.In a nozzle for a jet engine enclosed within a tubular housing andhaving a thrust reverser having a stowed position fixed relative to thetubular housing and having a deployed position and also having anexisting first stage mixer which includes a number of first stage lobesenclosed in said tubular housing rearward from said jet engine, a methodfor cooling hot exhaust engine exhaust gases and for attenuating engineexhaust noise comprising the steps of: utilizing a second stage mixercoupled to the exterior of said tubular housing at an exhaust apertureof said tubular housing; the second stage mixer being unenclosed by ahousing and having an exterior in contact with the ambient air to allowthe air to enter the mixer and mix with the gas from the first stagemixer; the second stage mixer having a trailing edge forming the exitterminus for the gas flow; and said thrust reverser in the deployedposition being positioned downstream of the exit terminus to reverse thegas flow; the second stage mixer receiving substantially all of theexhaust from the first stage mixer; and utilizing a plurality ofidentically formed lobes which equal in number those of the first stagelobes.
 22. The method according to claim 21 wherein the first stagelobes mix the hot exhaust gases with bypass air inside said tubularhousing to provide a cooler and lower flow velocity mixture thereof, andin which said step of utilizing the plurality of identically formedlobes comprises the steps of further mixing the cooler and lower flowvelocity mixture for further mixing thereof to level the disparate flowvelocities attendant therewith, to reduce the peak velocities of the hotexhaust gases, and to increase flow of the cooler and lower flowvelocity mixture whereby because noise is a function of jet exhaustvelocity to the 7th power and because peak velocities from the hotexhaust gases are reduced, the engine exhaust noise is thereby reduced.